Process for effecting the separation of a monoolefin from a diolefin



Dec. 30, 1947. l.. N. LEUM ET AL PROCESS. FOR EFFECTING THE SEPARATION OF A MONO-OLEFIN FROM A DOLEFIN' Filed July 23, 1943 Patented Dec. 30, 1947 Leonard N. Leumylipper Darby; Stephen J. MalV cu'ga, Lansdowne, and Saul ll. Kreps, Philadel phia, Pa., assignors` to The Atlantic Refining Quin-pany, Philadelphia, Pa.; a corporation-v of Pennsylvania Aspiimtin J'iyz, 1943, serial No. 495,949 14 claims: (c1. 2cm-sii) l This invention relates to the sepa-ration of hy-V drocarbon mixtures the components of'which are diiiicultly separable by ordinary fractionationmethods' by reason ofv the close relationship of their vapor pressures;V The invention is particu'' larly valuable as providing a practical and economical method 'for eiec'ting the isolation of isobutylene and butadiene from admixture' Withother hydrocarbons of four carbon atoms, i. el; alpha and beta butylene-'normal and iso-butano.

In the production of various products involving the use of isobutylene and/or butadiene, it has been found necessary to emplc'i'yv these compounds in substantially pure` form. Thus', inthe production of` butyl rubber by the reaction` of is-obutylene andbut'adiene, or of Vist'anexl by the homopolymerlzation of isobutylen'e, and inthe manufacture ofi high' molecular weight'isovbutylene polymersas' agents for increasing the Viscosity index o'r reducing the pour point of lubricating'- oil, the -i'sobutylene mustbe'of a rel-atively high degree of purity; Also, in'fthe production of high' anti-knock gasoline without the usey of tetraethyl leadbyv theA hydrogenation of iso-` octene, the iso-butylene! utilized in the prepara tion of the iso-octene mustbe substantially puree In the treatmentY ofcrackeddistillates,- itv is relatively easy; byv ordinary fractionation; toproduce a fractionconsistingl ofV orv predominatfin'g inv hydrocarbons of 'four carbon-atoms.- TheA pro'- duction of afractionAV consisting ofor predomi-A nating in hydrocarbons vo'f rive carb'onfatoms canlikewise be accomplished without great dic'ultyi by ordinary fractionation. The isolation of theA individual components oi-a'Ci or Cs hydrocarbon# 35I fraction by ordinary fractionation, however, is

commercially' impractical because of the very little diiference existing between the vapor pressures of the components of suchv ir'actions',.and'

other measures are consequently necessary.

Various methods have been heretofore proposed for effecting. the separation of hydrocarbon mixtures'containing components of similarvapor pressures; Most ofsuch methods do not provide'v for the separation of components of the same degree of` unsatur'ation, i. e., isobut'ylene" and`v alpha or beta butylene, and are further disa'dA vantageous in that they require special equipment such as towers containing. an inordinately large number of plates and/or costly or'dii'cultly procurable solvents for their executiom Other of the prior art' processes; while easily carried out in the laboratory do-notlend themselvesfto" For-f example', it' is'47V known that the separation-vof' butadlene'froin hy# commercial application drocarboii` mixtures containing butadiene to# gether with a' butylene may be readily achieved by treating the mixture with an' aqueous solution of cuprous chloride and ammonium chloride,r butadiene being selectively precipitated as an insoluble copper complex from whichv it is later regenerated. This method of recovering buta# diene from narrow boiling mixtures with butylene is not' adaptedto commercial scale operation,y whereinit is desirable to contact the solution andv mixture to beseparated in aI continuous counter-v current manner, because the insoluble butadienecopper complex clogs the tower, giving rise to extreme operating difficulties.

It is a principal object of the present'inVen-- tion to provide a= process for separating hydro'- carbons of similar vapor pressures which may be inexpensively operated in standard equipment, which does notentaill the employment of chemi' cal agents suchA as cuprousI chloride; and which does not depend for its successfulexecutio'n upon the selectivity characteristics of an auxiliary sol-vent.

The present invention, whereby the foregoing and other objects are achieved; is based on the discovery that-whenv a mixturev of olefins of similar vapor pressures, including one or more diiolens',-is'polymerized to yield a polymer mixture containing` Various polymers and copolymers of the' olelns and thev polymer mixture heated in' the presence of a'v depolymerization catalyst, thefcomposition of theresulting gasv depends on the temperature* employed.

'Ihe process" or thel invention may be utilized to" effect the separation ofV an iso-olen from a diolen, or of al normal olefin from afdio'lefin, or of bothV an iso-oleiin and a' normal olen from aldio'leiin, in which event the iso-olefin and normal olefin may be separated from each other. Although particularly adapted v'to' the' separation of Cif fractions, the process may be eiiectively applied, for exam-ple, to the't'reatment oiv a narrow boiling fraction comprising an iso-amylene" and/or a? normal amylene and a' pentadiene. Parain hydrocarbons `may or may notbe present in a mixture subjected to treatment. If present;- they are usuallyl separated as a'group.V

The' process will bef-particularly described as applied to th'eseparation of a narrow boiling hy`V dro'carbon mixture containing a dioleiin and both aniso# Aand a normaloleiin'.` Asso applied,` the process is executed by subjecting'-4 the mixture toA a polymerizationI treatment to eiect thesubstan'tia'lly` complete polymerization of the oleiinic components'V thereof, rcontacting the resulting 3 polymers with a depolymerization catalyst at a temperature sufficient to reproduce the iso-olefin in monomeric form, separating the reproduced monomeric iso-olefin from the unconverted polymers, contacting the unconverted polymers with a depolymerization catalyst at a temperature sufficient to reproduce the normal olen in monomeric form, and separating the reproduced monomeric normal olefin from the unconverted polymers still remaining.

The depolymerization catalysts which may be employed in the execution of the process include argillaceous adsorbents such as fullers earth, bentonite, acid activated bentonite or clay, bauxite, activated alumina, oxides or sulfides of metals of group VI of the periodic system, alkaline earth metal oxides, rare earth oxides, or mineral acids such as phosphoric acid, metaphosphoric acid or pyrophosphoric acid which may or may not be supported upon carriers such as diatomaceous earth, clay, titania, thoria, or the like. Of the catalysts mentioned, the clays are preferred because of their ready availability and relative cheapness.

The polymerization of the olenic components of the mixture to be separated may or may not involve the use of a polymerization catalyst. In effecting the separation of C4 fractions according to the invention, we have found it preferable, when carrying out the polymerization thermally in the absence of a catalyst, to maintain the operating temperature within the range of from 600 F. to l000 F. and to operate under a super-atmospheric pressure of from 500 to 21000 p. s. i. The thermal polymerization may be carried out in any suitable type of apparatus but usually a vertical reactor is employed in which the effluent gases can sweep high molecular weight polymers out of the reaction zone. Unless such provision is made for removal of heavy polymers, considerable coke formation may occur in the reaction vessel.

Following the polymerization of the olennic components, any paran hydrocarbons which may have been present in the original mixture are separated as by fractionation.

In the first of the two catalytic depolymerization treatments a temperature is preferably employed which does not give rise to the presence of more than minor amounts of monomeric normal olen and monomeric diolen in the gas resulting from the treatment. Such temperature is usually lower than the temperature at which the second catalytic depolymerization treatment is executed, and in the instance of a polymer mixture obtained by the polymerization of a mixture comprising isobutylene, butadiene, and a normal butylene, we have found it advantageous to maintain the operating temperature within the range of from 400 F. to 800 F., the optimum temperature depending primarily upon the depolymerization catalyst being employed. We have found in using fullers earth that a temperature of 600 F. to 800 F. gives the best results, while with a catalyst such as phosphoric acid on a diatbmaceous earth, a temperature of from 400 F. to 700 F. is recommended.

In the second depolymerization treatment, the catalyst may be the same as that employed in the first treatment, or a different catalyst may be used. Thus, the first treatment may be carried out using fullers earth or bentonite, and the second with one of the other catalysts mentioned. Most preferably, the temperature during the second depolymerization treatment is kept within the range of from 800 F. to 1000 F., but tem- :2,433,465 V fr peratures up to 1200 F. may be employed. Also it is possible to operate at a temperature lower than 800 F. depending upon the catalysts being used. Since we have found that dimeric butadiene tends to become converted to less desirable products at temperatures substantially in excess of 900 F., it is our practice in the separation of C4 hydrocarbon mixtures according to the invention, to execute the second depolymerization treatment at a temperature not substantially exceeding 900 F. when the polymer mixture contains dimeric butadiene.

The catalytic depolymerization treatments are preferably conducted at atmospheric pressure, but may be conducted at a subatmospheric or superatmospheric pressure. The rate of charge of the polymers to the heated catalyst, which may be contained within any suitable type of reaction vessel, may range from 0.5 to 5.0 volumes of polymers per volume of catalyst per hour. Upon becoming spent by reason of the accumulation of carbonaceous materials, the catalyst may be regenerated by treatment with an appropriate solvent or by calcination in the presence of air or by a combination of such methods.

The invention will be readily understood from the accompanying flow diagram in which minor elements such as pumps, valves, heat exchangers, condensers, and the like have been omitted for sake of simplicity. Proper placement of these auxiliaries will at once be evident to those skilled in the art to which the invention relates.

In explanation of the diagram, a hydrocarbon mixture of narrow boiling range, shown as a mixture of normal and isobutane with isobutylene, a normal butylene, and butadiene, is introduced into a tubular furnace l wherein the substantially complete polymerization of the olefinic constituents of the mixture is effected. The eiiiuent gas from the furnace comprising polymeric isobutylene, a polymer of the normal butylene, a copolymer of isobutylene and the' normal butylene, polymeric butadiene, and copolymers of butadiene and the monobutylenes, is led via line 2 to a fractionator 3 operated to separate the butanes and any unreacted olefins.

The bottoms from the fractionator 3 consisting of the polymerized olefins are conveyed, via line 4, to a tubular furnace or preheater 5 and thence to a column or chamber 6 which contains an appropriate quantity of a suitable depolymerization catalyst, for example, fullers earth. A gas containing monomeric isobutylene is withdrawn from the column 6 via line 1 to a fractionating column 8 wherein the monomeric isobutylene is separated.

Where as in the present case the polymer mixture conveyed to column 6 comprises an isoolen-normal olefin copolymer, all or a part of such copolymer may depolymerize along with the polymer of the iso-olefin. This has relatively little effect on the purity of the iso-olefin overhead of fractionator 8. Apparently the monomeric normal olen resulting from the depolymerization of the copolymer immediately repolymerizes with itself to yield homopolymers which are not depolymerizable at the temperatures at which column 6 is operated.

The unconverted polymers constituting the bottom product of the fractionating column 8 are conveyed via line 9 to a tubular furnace or preheater l0 and thence to a column ll which may be identical with column 6. The temperature at which column Il is operated is in all cases higher than the temperature at which'column E is op- .at a temperature which does not substantially exceed 900 F.

The monomeric normal butylene produced by the depolymerization reaction in column I l is separated by ractionator I2 to which the product of column l l is conveyed via line I3, The bottoms from the iractionating column I 2 comprise the butadiene polymers plus other polymers not reacted by either of the catalytic depolymerization treatments. These other polymers may be separated from the butadiene polymer by any suitable method after which the butadiene polymers may be cracked, if desired, to yield monomeric butadiene.

We have said that where the polymer mixture conveyed to column 6 comprises an iso-olefinnormal olen copolymer, all or part of such co.- polymer may be depolymerized therein, and that apparently the resulting monomeric normal olefin immediately repolymerizes with itself to yield homopolymers which are not depolymerizable at the temperatures at which column 6 is operated. It also seems apparent from `the results we have obtained that any monomeric diolein produced either as a consequence of the reaction in column 0 or as a consequence of the reactionin column ll immediately polymerizes additively to give homopolymers which do not depolymerize at the temperatures observed in the -operation of these columns. Our invention, however, is not predicated on the accuracy of any theory advanced herein.

Although the invention has been particularly described with reference to the separation of a hydrocarbon mixture containing both an iso-olefin and a normal olen, it will be understood that it is equally applicable to the separation of a mix-4 ture containing a diolen and one or more normal olens in the rabsence of an iso-olefin, or to a mixture comprising an iso-oleiin and a dioleiin in the absence of a normal olefin. Where the mixture to be separated contains an iso-olefin in the absence of any normal olen or vice versa, the second of the catalytic depolymerization units including the adjacent fractionator and preheater may be omitted, or if retained in order to increase through-put, may be operated at the same temperature as the first.

We claim:

1. A process for effecting the separation of a mono-olefin from a diolen of similar vapor pressure which comprises subjecting a mixture containing tlie mono-olefin and the diolefin to a nonselective polymerization treatment, contacting the resulting polymers with a depolymerization catalyst at a temperature sufcient to reproduce the mono-olen in monomeric form, and separating the reproduced monomeric mono-olefin from the unconverted polymers.

2. A process for effecting the separation of a hydrocarbon mixture containing an iso-olefin, a normal oleiin, and a diolefin of similar vapor pressures which comprises subjecting the mixture to a non-selective polymerization treatment, contacting the resulting polymers with a depolymerization catalyst at a temperature sufficient to reproduce thaise-olein in monomeric fom, ser# arating the reproduced monomeric iso--olen from the unconverted-polymers, contacting the unconverted polymers with a depolymerization catalyst at a temperature sufficient to reproduce the normal olen in monomeric form, and separating thel reproduced monomeric normal olefin from the unconverted polymers still remaining.

3. A process for effecting the separation of a mono-olen from a diolein of similar vaporpressure which comprises subjecting a mixture containing the mono-olefin and the diolen to a nonselective polymerization treatment, contacting the resulting polymers with a depolymerization catalyst at a temperature between 400 F. and 1200 F. to reproduce the mono-olen in monomeric form, and separating the reproduced monomeric mono-olefin from the unconverted polymers.

4. A process for effecting the separation of a hydrocarbon mixture containing an isoo1en, a normal olefin and a diolen of similar vapor pressures which comprises subjecting the mixture to a non-selective polymerization treatment, contacting the resulting polymers with a depolymerization catalyst at a temperature between 400 F. and 800 F. to reproduce the iso-olefin in monomeric form, separating the reproduced monomeric iso-olen from the unconverted polymers, contacting the unconverted polymers with a depolymerization catalyst at a temperature between 800 F. and 1200 F. to reproduce the normal olen in monomeric form, and separating the reproduced monomeric normal olefin from the unconverted polymers still remaining.

5. A process for effecting the separation of a mono-olefin of at least four carbon atoms from a diolen containing a like number of carbon atoms which comprises subjecting a mixture containing the mOIlO-Glen and the diolefn to a nonselective thermal polymerization treatment at a temperature between 600 F. and 1000 F. and at a superatmospheric pressure of from 500 p. s, i. .to 2000 p. s. i., contacting the resulting polymers with a depolymerization catalyst at a temperature between 400 F. and 900 F. to reproduce the mono-oleiin in monomeric form, and separating the reproduced monomeric mono-olefin from the unconverted polymers.

6. A process for effecting the separation of a hydrocarbon mixture containing an iso-olen, a normal olefin, and a diolen of similar vapor pressures which comprises subjecting the mixture to a non-selective thermal polymerization treatment at a temperature between 600 F. and l000 F. and at a superatmospheric pressure of from 500 to 2000 p. s. i., contacting the resulting polymers with a depolymerization catalyst at a temperature between 400 F. and 800 F. to reproduce the iso-olefin in monomeric form, separating the reproduced monomeric iso-olefin from the unconverted polymers, contacting the unconverted polymers with a depolymerization catalyst at a temperature between 800 F. and 900 F. to reproduce the normal olefin in monomeric form, and separating the reproduced monomeric normal olefin from the unconverted polymers still remaining.

'7. A process for effecting the separation of a butylene from butadiene which comprises subjecting a mixture containing the butylene and butadiene to a non-selective polymerization treatment, contacting the resulting polymers with a depolymerization catalyst at a temperature suiiicient to reproduce the butylene in monomeric form, and separating the reproduced monomeric butylene from the unconverted polymers.

8. A process for effecting the separation of a hydrocarbon mixture containing isobutylene,A a normal butylene, and butadiene which comprises subjecting the mixture to a `non-selective polymerization treatment, contacting the resulting polymers with a depolymerization catalyst at Aa temperature suflicient to reproducethe isobutylene in monomeric form, separating the reproduced monomeric isobutylene from the unconverted polymers, contacting the unconverted polymers with a depolymerization catalyst at a temperature sufficient to reproduce the normal butylene in monomeric form, and separating the reproduced monomeric normal butylene from the un- A converted polymers still remaining.

9. A process for effecting the separation of a butylene from butadiene which comprises subjecting a mixture containing the butylene and butadiene to a non-selective polymerization treatment, contacting the resulting polymers with a depolymerization catalyst at a temperature between 800 F. and 1200 F. to reproduce the butylene in monomeric form, and separating the reproduced monomeric butylene from the unconverted polymers.

10. A process for effecting the separation of a hydrocarbon mixture containing isobutylene, a normal butylene, and butadiene which comprises subjecting the mixture to a now-selective polymerization treatment, contacting the resulting polymers with a depolymerization catalyst at a temperature between 400 F. and 800 F. to reproduce the iscbutylene in monomeric form, separating the reproduced monomeric isobutylene from the unconverted polymers, contacting the uncon- Verted polymers with a depolymerization catalyst at a temperature between 800 F. and 900 F. to reproduce the normal butylene in monomeric form, and separating the reproduced monomeric normal butylene from the unconverted polymers still remaining.

11. A process for effecting the separation of a butylene from butadiene which comprises subjecting a mixture containing the butylene and butadiene to a non-selective thermal polymerization treatment at a temperature between 600 F. and 1000 F. and at a superatmospheric pressure of from 500 to 2000 p. s. i., contacting the resulting polymers with a depolymerization catalyst at a temperature between 400 F. and 900 F. to reproduce the butylene in monomeric form, and separating the reproduced monomeric butylene from the unconverted polymers.

12. A process for effecting the separation of isobutylene from butadiene which comprises subjecting a mixture containing isobutylene and butadiene to a non-selective thermal polymerization treatment at a temperature between 600 F. and

1000v F. and at a superatmospheric pressure of from 500 tor2000 p. s. i., contacting the resulting polymers with a depolymerization catalyst at a temperature between 400 F. and 800 F. to reproduce the iso-butylene in monomeric form, and separati'n'g the reproduced monomeric iscbutylene from the unconverted polymers.

13. A process for eecting the separation of a normal butylene from butadiene which comprises subjecting a mixture containing the normal butylene and butadiene to a non-selective thermal polymerization treatment at a temperature between 600 F. and 1000 F. and at a superatmospheric pressure of from 500 to 2000 p. s. i., contacting the resulting polymers with a depolymerization catalyst at a temperature between 800 F. and 900 F. to reproduce the normal butylene in monomeric form, and separating the reproduced monomeric normal butylene from the unconverted polymers.

14. A process for effecting the separation of a hydrocarbon mixture containing isobutylene, a normal butylene, and butadiene, which comprises subjecting the mixture to a non-selective thermal polymerization treatment at a temperature between 600" F. and 1000 F. and at a superatmospheric pressure of from 500 to 2000 p. s. i., contacting the resulting polymers with a depolymerization catalyst at a temperature between 400 F. and 800 F. to reproduce the isobutylene in monomeric form, separating the reproduced monomeric isobutylene from the unconverted polymers, contacting the unconverted polymers with a depolymerization catalyst at a temperature between 800 F. and 900 F. to reproduce the normal butylene in monomeric form, and separating the reproduced monomeric normal butylene from the unconverted polymers still remaining.

LEONARD N. LEUM.

STEPHEN J. MACUGA.

SAUL I. KREPS.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,282,906 Mersereau Oct. 29, 1918 2,222,055 Ward Nov. 19, 1940 2,178,808 Rosen etal. Nov. 7, 1939 1,894,661 Brooks J an. 17, 1933 2,320,127 Hachmuth May 25, 1943 2,152,908 Morrell et al. Apr. 4, 1939 2,398,930 Gary Apr. 23, 1946 FOREIGN PATENTS Number Country Date 9,722 Great Britain Apr. 22, 1912 

